The 100-Year Rainfall/1000-Year Flood

All of us have been touched by the stories of the Colorado floods. This particular natural disaster is occurring in an area not known for flooding. We are used to hearing about fires, or mudslides, or avalanches in Colorado. But while floods are apparently not uncommon in Boulder, I think most people assume “high and dry” when they think “Colorado”.

According to NOAA, a cold front stalled over the state, and came into contact with monsoonal air. The clash between the two led to heavy, heavy rain. Colorado’s Front Range was hit, from Colorado Springs north to Fort Collins. Boulder County was hit the hardest. By September 12th, 9.08 inches of rain was recorded there. That number nearly doubled to 17 inches by September 15th. Seventeen inches is about the average annual rainfall for a year. In other words, in a 3 three-day period, this area was inundated with the same amount of rain it would normally have had spread throughout one year.

One of the difficulties when you’re far away from an event and trying to understand is finding sources for information that are informative and accurate. Colorado happens to be home of some of the most interesting environmental studies programs in the country, one of which is at the University of Colorado Boulder. Professor Roger Pielke Jr.’s Blog is a good place to start. Professor Pielke is a professor at the Center for Science and Technology Policy Research at the University of Colorado Boulder. If you click around his blog posts, you’ll quickly find other interesting analyses.

Something Professor Pielke talks about here is the notion of a 100-year flood and the misunderstandings that arise with the use of the N-year flood terminology. The “100-year flood” is something you’ll see a lot of if you search the internet for information about the Colorado floods, along with the “1000-year flood”. It appears that what Colorado has experienced is a 1000-year rainfall, and a 100-year flood. What this means is that such a large rainfall in that area has a 0.1% chance of being exceeded in any given year, and the flood they experienced is one that has only a 1.0% chance of being exceeded in any given year. While we sometimes refer to the N-year event, it’s also frequently critiqued for being confusing because people often think it means that such events will only happen once in a 100 years. In fact, as Professor Pielke explains, this is not the case. There’s no doubt that Colorado has suffered a bad flood, and a bad rainfall, but the terms 100-year and 1000-year have nothing to do with the idea that these weather events will only happen once in a hundred years or once in a thousand years.

First, the use of the N-year to describe the possibility of an event occurring in any given year is pretty deeply embedded in a lot of our flood control and emergency management policies. See for example, the way it is used for determining flood zones by FEMA.

Second, the use of any N-year term in all its ambiguity and confusion is loaded with symbolic meaning, and not just what the mass media and some policymakers propagate. While I can only speak of this anecdotally, my experience with victims of the 2011 Mississippi floods is that immediately after the event and for at least a year later, the terminology was like a life-preserver on an emotional level for some of them. For some, it gave validation that they had experienced something not only horrific and but also highly unusual. At a point when it was very important to believe that normalcy could be restored, it seemed to me that the unusualness of the situation provided them with hope and a will to move forward with rebuilding. Now, two years later, I’ve heard some mull over the term, noting that they had not understood it correctly at the time, and quite consciously concerned about what it will mean for river management in the future. Part of their continuing attention is due to a call for new policymaking along the river, but part of it is because they’ve had time to learn about the various issues that gave rise to the flood and the difficulties of river management. They are continuing to process the experience while still living through its aftermath. The meaning has changed for them, but they needed some distance from the critical event itself in order to begin to think through its many implications for their future.

While I don’t know the degree to which the term is being used in Colorado’s disaster victims (and would invite comments about the meaning of this term to the people who experienced the rainfall), it is certainly being used in the press. And, it will have symbolic power not only for those who use it in the press, but also for all who hear it. Those of us who use the term because of its salience in public policy need to deploy it with caution. At the same time, being too quick to dismiss the emotional importance of the term to those who are dealing with the stress of living through a disaster may also be damaging to the disaster management processes that needs to take place in any setting where a natural disaster has occurred, including Colorado.

I hope everyone becomes skeptical of the term and learns to listen carefully when they hear it, to discern how it is being deployed by the speakers and asking themselves what the speaker’s goal is in using it. It would be nice if we would stop using N-year measures altogether, but since FEMA and other organizations use it for disaster planning and to describe weather events, we’re probably stuck with it for quite some time.

But it can be deeply misleading, and one place it leads people is to the idea that, once they’ve recovered from a disaster, it will not happen again in their lifetime — or their children’s. Or in their children’s children’s future. Unfortunately, it may. Where it has flooded once, it can flood again. Even a small amount of flooding can cause vulnerable populations to lose everything they have built in their lives for some length of time, setting them back several years financially. An extreme flood can wipe out generations of wealth building. In the decisions that will follow concerning rebuilding and recovery, thinking through what the term means for the people living where the event has just occurred who may be facing it for the first time, will be incredibly important to gaining support for rebuilding in a way that will make everyone safer. And, knowing that there will likely be a learning curve in understanding flooding, flood management and flood control, strikes me as an essential element in the task ahead of disaster managers and policymakers.

A great deal of ink has been spilled on all these ideas and from a wide variety of perspectives, but for some further reading complexities of flood management and the symbolic power of terminology in environmental policy, here are some places to look:

T.A. Birkland (2007). Lessons of Disaster: Policy Change After Catastrophic Events. Georgetown University Press.

T.A. Birkland (1997/2007). After Disaster: Agenda Setting, Public Policy and Focusing Events. Georgetown University Press.

S.D. Brody, S. Zahran, P. Maghelal, H. Grover, and W.E. Highfield (2007). The Rising Costs of Floods: Examining the Impact of Planning and Development Decisions on Property Damage in Florida. Journal of the American Planning Association 73(3): 330-345.

B. Merz, J. Hall, M. Disse and A. Schumann (2010). Fluvial Flood Risk Management in a Changing World. Natural Hazards and Earth System Sciences 10: 509-527.

R.A. Pielke (1999). Nine Fallacies of Floods. Climate Change 42: 413-438.

K. Tierney, C. Bevc and E. Kuligowski (2006). Metaphors Matter: Disaster Myths, Media Frames, and Their Consequences in Hurricane Katrina. The Annals of the American Academy of Political and Social Science 604(1): 57-81.

Welcome to our blog!


The idea behind this blog is simple: to provide a forum for discussion about disasters of all kinds and a place where a broad audience can find information about the latest policies, legal developments and research concerning disaster mitigation, management, and recovery. We hope this blog will be an avenue for researchers to broaden their audience beyond academic settings, but we also would like it to be a place where more than an academic perspective is represented.

While the idea seems simple, it’s complexities are obvious when you consider all the voices that can be a part of this discussion!

There are many individuals thinking and writing about disaster policy, the effects of disasters on various populations, and the difficulties of disaster mediation and recovery. They provide a wide variety of viewpoints, including those who have been caught in a disaster; activists interested in helping disaster victims; and analysts ranging from a remarkable number of perspectives including (but not limited to) political scientists, sociologists, economists, historians, novelists, folklorists, policymakers, lawyers and journalists. And those are just a few we have encountered in the last two years!

So, given the challenges, what motivates us to pursue our simple idea in all its complexity?

When we began researching disasters, we were quickly and painfully aware of the absence of a forum where multiple views were exchanged. Yet as interdisciplinary researchers who do the sort of work that requires us to talk with our research participants (flood victims, mostly), we desperately wanted to find and hear multiple perspectives from as many perspectives as possible. The absence of such a forum alarmed us for many reasons, not least of all because we feared that important ideas and insights were slipping through the cracks as everyone talked amongst themselves and not with each other.

We want to facilitate those conversations in part because we have heard, while doing our research and presenting it at conferences, so many ideas from so many people. We want them heard — and we want them heard by other people who are thinking about, writing and working on issues around disaster politics. And, on a more selfish level, we want to talk back!

That said, this is not just a blog about disaster studies, though this academic area of study will frame much of what appears here. It’s also a blog about the people who are affected by disasters, which in the twenty-first century, is nearly everyone.

About our regular contributors and our interests

My name is Laura Hatcher, and I am currently a writer, independent researcher and a consultant. My own personal intellectual obsession and what I have published about the most has to do with the historical development of regulation of private property. Importantly for disaster studies, much time, effort and thought has been put into policies that are designed (not always explicitly) to protect property and the interests of ownership. Whose property, and what type of ownership receives protection or, alternatively is sacrificed, are interesting questions I hope to explore here with you. They have far-reaching implications for much emergency management policy, not to mention flood control, and various insurance regimes, including fire, wind, hail… And financial disasters, too! While one may think “property” narrows our scope, in fact, it does not when you consider the wide variety of property we have available in our society, all of which can be impacted by various disaster scenarios. “Property” gives us an anchor and a frame to help us sort and prioritize our work here, but it is not intended to narrow us too much.

Indeed, the other two regular contributors have slightly different interests. Randy Burnside, Associate Professor of Political Science and Director of the MPA program at Southern Illinois University, is a nationally recognized expert in emergency management. After watching friends and family struggle with recovery in post-Katrina New Orleans, Randy has spent a great deal of time thinking about and studying the politics of managing disaster contexts. Logan Strother, a doctoral fellow at Syracuse University, is particularly interested in civil liberties and bureaucratic behavior. Together, the three of us are co-authoring research on the Mississippi Levee System. Separately, we maintain some very different worldviews. We also bring different skill sets to our work, and so we range in methods from quantitative to qualitative, mixed methods and textual interpretation. The research we discuss here, then, will also range across methods and methodologies. Both Randy and Logan will also serve as the associate editors of this blog, helping me think through editorial decisions as well as providing content and facilitating discussions.

This blog has been a long time in coming, and Randy, Logan and I are all thrilled it is finally here. We hope you find it interesting, helpful and useful. Over the next few weeks we’ll be adding more content, including links to other relevant blogs, reviews of research, analyses of court cases, and lots of other things. In addition, we have a few guest contributors lined up. We will be posting 2-3 times a week as we get started. Check back often!

We welcome your input and comments! 

If you have an idea for a blog post, or would like us to consider a particular topic, just email me at We will certainly consider your ideas! If you have a specialty related to the topics of this blog, introduce yourself! But beware! We might ask you to contribute a post!

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A note on the photo at the top of this post

The photo comes courtesy of John Story, of Wolf Island Farms, Missouri. It’s a photo of the shop on his farm, a few days after the activation of the Birds Point/New Madrid spillway. Take a careful look — the scum line at the back shows how high the water was. You’ll be reading about the floods of 2011. All of us were residents of southern Illinois, parts of which were hit very hard, at the time of the 2011 flood. All three of us have been interested in flood recovery issues on both sides of the river and have been watching the new policymaking that is ongoing for the levee system. Because it encapsulated all those issues, the photo seemed especially appropriate for our blog launch. We thank Mr. Story for providing the picture!